Robotic surgical system with contact sensing feature

ABSTRACT

A method of monitoring contact between a probe and a tissue surface includes placing the probe in proximity to the surface, robotically moving the probe, measuring a tissue parameter at the distal end of the probe, calculating an amount of change in the measured tissue parameter between measurements thereof, and indicating a change in proximity or degree of contact between the probe and the surface based upon the amount of change. The indication of change may be based directly upon the calculated amount of change in the measured parameter or upon a calculated rate of change in the parameter. The rate of change may be relative to the time between measurements or the distance traveled by the probe between measurements, and may be calculated as a first, second, or other derivative of the tissue parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application No. 60/851,042, filed 12 Oct. 2006, which is hereby expressly incorporated by reference as though fully set forth herein.

This application is a continuation-in-part of U.S. application Ser. No. 11/139,908, filed 27 May 2005 (the '908 application), now pending, which claims the benefit of U.S. provisional application No. 60/575,741, filed 28 May 2004 (the '741 application). The '908 and '741 applications are hereby expressly incorporated by reference as though fully set forth herein.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The instant invention relates to robotically controlled medical devices. In particular, the instant invention relates to a robotic surgical system for navigating a medical device through a patient's body for diagnostic and therapeutic purposes.

b. Background Art

Catheters are used for an ever growing number of medical procedures. To name just a few examples, catheters are used for diagnostic, therapeutic, and ablation procedures. Typically, the user manually manipulates the catheter through the patient's vasculature to the intended site, such as a site within the patient's heart. The catheter typically carries one or more electrodes or other diagnostic or therapeutic devices, which may be used for ablation, diagnosis, cardiac mapping, or the like.

It is well known that, to facilitate manipulation of the catheter through the patient's vasculature to the intended site, portions of the catheter shaft, especially the distal regions thereof, may be made steerable. For example, the catheter may be manufactured such that the user can translate, rotate, and deflect the distal end of the catheter as necessary and desired to negotiate the tortuous paths of the patient's vasculature en route to the target site. Navigating a catheter reliably through the patient's body to a precise location, however, is an extremely tedious process requiring a substantial amount of time and skill and potentially causing a high degree of fatigue in the physician, especially where actuation forces are transmitted over large distances.

BRIEF SUMMARY OF THE INVENTION

It is thus desirable to be able to navigate a medical device accurately and precisely through a patient's body to the locations of diagnostic or therapeutic interest.

It is also desirable to be able to reduce the fatigue factor associated with navigating a medical device through a patient's body.

It is further desirable to be able to preserve the ability to manually navigate a medical device when so desired.

It is also desirable that the medical device be able to distinguish proximity or degree of contact between the medical device and a tissue surface.

According to a first aspect of the invention, a method of monitoring contact between a probe and a tissue surface includes the steps of: placing the probe in proximity to the tissue surface; robotically moving the probe; measuring a tissue parameter at the distal end of the probe using a sensor at the distal end of the probe; calculating an amount of change in the measured tissue parameter between successive measurements thereof; and indicating a change in proximity or degree of contact between the probe and the tissue surface based upon the amount of change in the measured tissue parameter. The tissue parameter may be selected from the group consisting of impedance, phase angle, electrogram amplitude, optical feedback, and ultrasonic feedback.

The step of indicating a change in proximity or degree of contact optionally includes: indicating no change when the amount of change in the tissue parameter falls within a pre-determined range of values; and indicating a change when the amount of change in the tissue parameter falls outside the pre-determined range of values. The pre-determined range of values may be user selectable. Alternatively, the step of indicating a change in proximity or degree of contact includes: comparing the amount of change in the tissue parameter to a change threshold; indicating no change when the amount of change in the tissue parameter is less than the change threshold; and indicating a change when the amount of change in the tissue parameter is greater than the change threshold. The change threshold may be user selectable.

Alternatively, the step of indicating a change in proximity or degree of contact may be based upon a rate of change in the measured tissue parameter, which may be a derivative of the measured tissue parameter with respect to time or with respect to a distance the probe moves between successive measurements of the tissue parameter. Indicating a change in proximity or degree of contact based upon the rate of change may include: indicating no change when the rate of change falls within a pre-determined range of values; and indicating a change when the rate of change falls outside the pre-determined range of values. The pre-determined range of values may be user selectable. Alternatively, it may include: comparing the rate of change to a rate of change threshold; indicating no change when the rate of change is less than the rate of change threshold; and indicating a change when the rate of change exceeds the rate of change threshold. The rate of change threshold may be user selectable.

In another aspect of the invention, a method of monitoring contact between a probe and a tissue surface includes the steps of: navigating the probe into a body of a patient; moving the probe within the body using a calibrated system; monitoring a tissue parameter using a sensor at the distal end of the probe for an indicator of proximity or degree of contact between the probe and the tissue surface; and reporting a change in proximity or degree of contact between the probe and the tissue surface based upon the monitored tissue parameter. As part of the monitoring step, the tissue parameter may be measured periodically or episodically. The calibrated system may be a robotically controlled system.

The monitoring step may include monitoring the tissue parameter for an indicator of a change in proximity or degree of contact between the probe and the tissue surface. The change may be a change indicative of the probe making contact with the tissue surface, a change indicative of the probe breaking contact with the tissue surface, or a change indicative of a change in the degree of contact between the probe and the tissue surface. Similarly, the reporting step may indicate contact between the probe and the tissue surface, no contact between the probe and the tissue surface, or a change in the degree of contact between the probe and the tissue surface.

In some implementations of the method, the value of the tissue parameter may be monitored to determine when it crosses a threshold value indicative of the change in proximity or degree of contact. Alternatively, changes in the value of the tissue parameter may be monitored for crossing of a threshold value. In yet another alternative, a rate of change in the tissue parameter is monitored for crossing of a threshold value; the rate of change may be a first derivative or a second derivative of the tissue parameter. A change in proximity or degree of contact may be reported when the monitored variable crosses (e.g., exceeds) the threshold value, and may not be reported when the monitored variable does not cross (e.g., is less than) the threshold value.

In yet another embodiment of the invention, a surgical system includes: a probe for introduction into a body of a patient; a robotically-controlled system to move the probe within the body of the patient; a sensor carried on the probe for measuring a parameter of a tissue surface; and a processor programmed to monitor the parameter and indicate a change in proximity or degree of contact between the probe and the tissue surface based on a change in the parameter between successive measurements. Optionally, the sensor is an electrophysiology sensor. The processor may compare the change in the parameter between successive measurements thereof or a rate of change in the parameter to a pre-determined range of values and indicate a change in proximity or degree of contact when the change in the parameter or the rate of change in the parameter falls outside the pre-determined range of values. Alternatively, the processor may compare the change in the parameter between successive measurements thereof or a rate of change in the parameter to a threshold value and indicate a change in proximity or degree of contact when the change in the parameter or the rate of change in the parameter crosses (e.g., exceeds) the threshold value.

In still another embodiment of the invention, a surgical system includes: a probe for introduction into a body of a patient; a locally-calibrated system to move the probe within the body of the patient; a sensor carried on the probe for measuring a parameter of a tissue surface; and a processor programmed to monitor the parameter and indicate a change in proximity or degree of contact between the probe and the tissue surface based on a rate of change in the parameter between successive measurements thereof. The rate of change may be monitored by calculating a first or second derivative of the tissue parameter, and may be a time rate of change or a rate of change with respect to probe distance traveled.

An advantage of the present invention is a reduced exposure to radiation for both the patient and the physician, since the present invention reduces the time required to navigate the catheter to a target location and minimizes the need for fluoroscopy to locate the catheter within the patient.

Another advantage of the present invention is the ability to easily switch between automated robotic control and manual control of the catheter.

Still another advantage of the present invention is the ability to remotely interact with the robotic surgical system controlling the catheter.

The foregoing and other aspects, features, details, utilities, and advantages of the present invention will be apparent from reading the following description and claims, and from reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an embodiment of a robotic surgical system.

FIG. 2 is a perspective view of one embodiment of a catheter holding device with a catheter placed therein.

FIG. 3 is an end view of the catheter holding device of FIG. 2.

FIG. 4 is a perspective view of one embodiment of a catheter holding device with a catheter secured therein.

FIG. 5 is an end view of the catheter holding device of FIG. 4.

FIG. 6 illustrates an exemplary steerable catheter such as may be used in the robotic surgical system.

FIG. 7 depicts automatic control of the robotic surgical system according to a predetermined program.

FIG. 8 depicts a user manually controlling the robotic surgical system via an input device.

FIG. 9 depicts the user of FIG. 8 manually controlling the steerable catheter after having removed it from the robotic surgical system.

FIG. 10 schematically illustrates a contact sensing surgical system.

FIG. 11 is a high-level flowchart of a contact sensing methodology.

FIGS. 12a through 12o illustrate alternative implementations of the decision process for indicating a change in proximity or degree of contact in the high-level flowchart of FIG. 11.

FIG. 13a is an exemplary plot of tissue parameter versus either time or probe distance as measured by a contact sensing surgical system.

FIG. 13b is the derivative of the plot in FIG. 13 a.

DETAILED DESCRIPTION OF THE INVENTION

Robotic Surgical System

FIG. 1 schematically illustrates an embodiment of a robotic surgical system 10 for robotic manipulation and control of a medical device 12. Medical device 12 is preferably a catheter, which may be any type of catheter, including, by way of example only and without limitation, an ablation catheter, a guide wire catheter, an introducer catheter, a probe, or a stylet. It should be understood, however, that any other therapeutic, diagnostic, or assistive medical device may be controlled by robotic surgical system 10 without departing from the scope of the present invention. Such other devices include, but are not limited to, syringes, electrophoresis devices, iontophoresis devices, transdermal pharmaceutical delivery devices, myoblast delivery devices, stem cell delivery devices, ablation devices, stents, and pacemaker leads, which may be carried on or delivered by a catheter. It should further be understood that robotic surgical system 10 may be used to manipulate and control more than one medical device 12 in accordance with the quick installation and removal feature described herein. Accordingly, the terms “medical device,” “probe,” “therapeutic device,” and “catheter” are used interchangeably herein.

Robotic surgical system 10 generally includes a track 14, a catheter holding device 16, a translation servo mechanism 18, a catheter deflection control mechanism 20, a deflection servo mechanism 22, and a controller 24 operatively coupled to at least one of translation servo mechanism 18 and deflection servo mechanism 22. Translation and deflection servo mechanisms 18, 22 may be any type of device for providing mechanical control at a distance, including continuous motors, stepper motors, hydraulic actuators, pulley systems, and other devices known to those of ordinary skill in the art. Catheter deflection control mechanism 20 and deflection servo mechanism 22 are collectively referred to herein as a “catheter deflection mechanism.”

Catheter holding device 16 includes a catheter receiving portion 26. Catheter receiving portion 26 is configured to receive catheter 12 by installing a catheter control handle 28, located near a proximal end 30 of catheter 12, into catheter receiving portion 26. Preferably, catheter receiving portion 26 is adapted for quick installation and removal of any type of catheter 12 (or, as noted above, another medical device), thereby facilitating the installation of device 12 for control by robotic surgical system 10 and removal of device 12 for manual control (e.g., user manipulation of catheter control handle 28). Accordingly, catheter control handle 28 may be secured in catheter receiving portion 26 by a frictional fit or with one or more quick-release fasteners. Alternatively, the inner surface of catheter receiving portion 26 and the outer surface of catheter control handle 28 may include mating threaded portions to permit catheter control handle 28 to be screwed into catheter holding device 16. In other embodiments of robotic surgical system 10, catheter control handle 28 is clamped or strapped in place in catheter receiving portion 26. An adapter may also be used to facilitate the reception of catheter control handle 28 within catheter receiving portion 26.

One embodiment of catheter holding device 16 is illustrated in FIGS. 2 and 3 with catheter control handle 28 placed, but not secured, therein. Catheter holding device 16 includes a base plate 32 and a plurality of upstanding support plates 34. Support plates 34 support cams 36, which are connected to pulley systems 38.

Catheter control handle 28 is received downwardly through an opening into the catheter receiving portion 26 and onto belts 40 of pulley systems 38. As catheter control handle 28 is urged downwardly, belts 40 rotate upper and lower pulleys 38 a, 38 b in the direction of arrows a. This, in turn, urges cams 36 downwards via links 42 and draws upper pulleys 38 a, 38 b towards one another via links 44, while simultaneously wrapping the belts 40 about catheter control handle 28. Catheter control handle 28 is thereby secured within catheter receiving portion 26 as shown in FIGS. 4 and 5. To remove catheter control handle from catheter holding device 16, the user need only release cams 36, which reverses the process described above and opens catheter receiving portion 26.

Catheter holding device 16 is translatably associated with track 14. The phrase “translatably associated with” encompasses all types of relative lateral motion between catheter holding device 16 and track 14. For example, catheter holding device 16 may slide relative to track 14. Alternatively, catheter holding device 16 may move laterally along a screw mechanism 46, such as a worm gear, a lead screw, or a ball screw, attached to track 14. Preferably, catheter holding device 16 has a translation range relative to track 14 (i.e., the lateral distance that catheter holding device 16 can travel relative to track 14 between extremes) of at least about 5 cm, the approximate width of a human heart. More preferably, the translation range of catheter holding device 16 relative to track 14 is at least about 10 cm.

In the preferred embodiment of the invention, a carriage 48 is translatably mounted on track 14 via screw mechanism 46. Catheter holding device 16 is mounted on carriage 48 such that catheter holding device 16 translates relative to track 14 with carriage 48. For example, base plate 32 may be fixedly or removably mounted on carriage 48. Alternatively, catheter holding device 16 may be integrally formed with carriage 48 as a single assembly (i.e., base plate 32 and carriage 48 may be a single, unitary component). Likewise, in some embodiments of the invention, catheter holding device 16 may be translatably mounted directly on track 14 without an intervening carriage.

Translation servo mechanism 18 is operatively coupled to catheter holding device 16 and adapted to control translation of catheter holding device 16 relative to track 14 in order to adjust the lateral position of catheter holding device 16 along track 14. Preferably, translation servo mechanism 18 is operatively coupled to carriage 48 in order to move carriage 48, and therefore catheter holding device 16 mounted thereon, laterally along track 14. In the embodiment shown in FIG. 1, translation servo mechanism 18 drives screw mechanism 46, thereby moving carriage 48 laterally therealong.

Deflection servo mechanism 22 is operatively coupled to and adapted to control catheter deflection control mechanism 20. In the preferred embodiment of the invention, deflection servo mechanism 22 is operatively coupled to catheter deflection control mechanism 20 such that deflection servo mechanism 22 can rotate catheter deflection control mechanism 20. Either or both of deflection servo mechanism 22 and catheter deflection control mechanism 20 may be mounted on carriage 48 in order to simplify the transmission system linking deflection servo mechanism 22 and catheter deflection control mechanism 20. In some embodiments of robotic surgical system 10, catheter deflection control mechanism 20 is incorporated in catheter holding device 16, for example by utilizing pulley systems 38, and in particular belts 40, as further described below. One of ordinary skill in the art will appreciate, however, that catheter deflection control mechanism 20 may also be separated from catheter holding device 16 without departing from the spirit and scope of the present invention.

Controller 24 is adapted to control at least one of translation servo mechanism 18 and deflection servo mechanism 22 in order to navigate catheter 12 received in catheter holding device 16. It should also be noted that the use of multiple controllers to control translation servo mechanism 18 and deflection servo mechanism 22 is regarded as within the scope of the present invention. Throughout this disclosure, the term “controller” refers to a device that controls the movement or actuation of one or more robotic systems (that is, the component responsible for providing command inputs to the servo mechanisms). One of ordinary skill in the art will understand how to select an appropriate controller for any particular mechanism within robotic surgical system 10. Further, the term “controller” should be regarded as encompassing both a singular, integrated controller and a plurality of controllers for actuating one or more robotic systems.

As shown in FIG. 6, catheter 12 is preferably a steerable catheter including at least one pull wire 50 extending from catheter control handle 28 near proximal end 30 of catheter 12 to a distal end 52 of catheter 12. Pull wires 50 may be coupled to at least one pull ring 54, also located near distal end 52 of catheter 12. When placed in tension, pull wires 50 deflect distal end 52 of catheter 12 into various configurations. As one of skill in the art will understand, additional pull wires 50 will enhance the deflection versatility of distal end 52 of catheter 12. For example, a single pull wire 50 with a single point of attachment to pull ring 54 will permit distal end 52 of catheter 12 to deflect on a single axis, and perhaps in only one direction, for example upwards relative to FIG. 6. By adding a second pull wire 50 (as shown in FIG. 6), or by looping a single pull wire 50 to have two points of attachment 56 to pull ring 54, distal end 52 of catheter 12 may be deflected in two directions, for example both upwards and downwards relative to FIG. 6. A catheter 12 with four pull wires 50 attached to pull ring 54 at about 90° intervals can deflect in four directions, for example upwards, downwards, and into and out of the plane of the paper relative to FIG. 6.

One or more catheter deflection actuators 58 may be provided on catheter control handle 28 to selectively tension one or more pull wires 50, thereby controlling the direction and degree of deflection of distal end 52 of catheter 12. In some embodiments, one or more knobs may be provided, rotation of which selectively tension one or more pull wires 50. It should be understood, however, that catheter deflection actuators 58 may take many other forms, including, but not limited to, sliders and switches, without departing from the spirit and scope of the present invention. Additionally, it is contemplated that rotating catheter control handle 28 itself may selectively tension pull wires 50 and deflect distal end 52 of catheter 12.

Returning to FIG. 1, when catheter control handle 28 is received within catheter receiving portion 26, catheter 12 translates relative to track 14 with catheter holding device 16, thereby providing a first degree of freedom permitting catheter 12 to be advanced into and retracted from a patient's body. Additionally, catheter 12 is operatively coupled to catheter deflection control mechanism 20 such that actuation of catheter deflection control mechanism 20 causes distal end 52 of catheter 12 to deflect, thereby providing a second degree of freedom to catheter 12. In particular, catheter deflection actuator 58 may be operatively coupled to catheter deflection control mechanism 20 such that catheter deflection control mechanism 20 can actuate catheter deflection actuator 58 to selectively tension one or more pull wires 50 and deflect the distal end 52 of catheter 12 by a desired amount in a desired direction.

In some embodiments of the invention, rotating catheter deflection control mechanism 20 will rotate catheter deflection actuator 58 in turn, thereby selectively tensioning one or more pull wires 50 within catheter 12. The transmission system between catheter deflection control mechanism 20 and catheter deflection actuator 58 may be a frictional fit provided, for example, by rubberized coatings surrounding catheter deflection control mechanism 20 and catheter deflection actuator 58. Alternatively, catheter deflection control mechanism 20 and catheter deflection actuator 58 may be coupled with mating gear teeth or knurling.

Referring specifically to the embodiment of catheter holding device 16 depicted in FIGS. 2-5, when catheter 12 is secured in catheter receiving portion 26, belts 40 frictionally engage catheter control handle 28. They may also engage catheter deflection actuator 58. Thus, if pulley system 38 is driven by deflection servo mechanism 22, belts 40 may rotate catheter control handle 28, catheter deflection actuator 58, or both, in order to selectively tension one or more pull wires 50 and deflect distal end 52 of catheter 12.

It should be understood that the particular configurations of catheter deflection control mechanism 20 and catheter deflection actuator 58 described above are merely exemplary and can be modified without departing from the spirit and scope of the invention. For example, if catheter deflection actuator 58 is a slider rather than a knob, catheter deflection control mechanism 20 may be suitably modified, or even replaced as a modular unit, to actuate a slider. This facilitates the quick connect/disconnect operation of robotic surgical system 10 by allowing easy installation and interconnection between off-the-shelf medical devices of varying construction and robotic surgical system 10.

As described above, the inclusion of additional pull wires 50 in catheter 12 increases the number of directions in which distal end 52 of catheter 12 can deflect. This is referred to herein as “deflection versatility.” Where relatively few pull wires 50 (e.g., fewer than about four pull wires 50) are used, however, compensation for lost deflection versatility may be had by rotating catheter 12 about its axis. For example, in a catheter using only a single pull wire 50 with a single point of attachment to pull ring 54, permitting the catheter to deflect only in one direction, the catheter may be deflected in the opposite direction simply by rotating it 180° about its axis. Similarly, a catheter that can deflect in two directions 180° apart can be deflected in the directions midway therebetween by rotating the catheter 90° about its axis.

Accordingly, in some embodiments of the invention, catheter receiving portion 26 is rotatable. An example of such a rotatable catheter receiving portion is catheter receiving portion 26 defined by pulley system 38 depicted in FIGS. 2-5. A rotation servo mechanism 60 is operatively coupled to rotatable catheter receiving portion 26 and adapted to control rotatable catheter receiving portion 26. Thus, pulley system 38 may be driven by rotation servo mechanism 60, thereby engaging belts 40 to rotate catheter 12 about its axis.

If desired, rotation servo mechanism 60 may be mounted on carriage 48 or affixed to catheter holding device 16 such that rotation servo mechanism 60 translates relative to track 14 with catheter holding device 16. This arrangement creates a fixed-distance relationship between rotation servo mechanism 60 and catheter holding device 16, which can simplify the transmission system coupling rotation servo mechanism 60 to catheter holding device 16.

When installed in catheter holding device 16, catheter 12 rotates with catheter receiving portion 26, thereby providing a third degree of freedom to catheter 12 and compensating for low deflection versatility attributable to a relatively lower number of pull wires 50. Catheter receiving portion 26 is preferably rotatable at least about 360° about its axis, such that catheter 12 received therein is also rotatable at least about 360° about its axis, thereby facilitating deflection of distal end 52 of catheter 12 in substantially any direction, significantly enhancing the deflection versatility of the distal end 52 of the catheter 12. Catheter receiving portion 26 may also be designed to rotate about 720° or more about its axis.

Rotating catheter 12 by rotating catheter receiving portion 26 may cause inadvertent deflection of distal end 52 of catheter 12. As one skilled in the art will recognize from this disclosure, as catheter receiving portion 26 and catheter 12 rotate, catheter deflection actuator 58 may remain stationary, rather than rotating with catheter control handle 28, if the torque applied by rotation servo mechanism 60 is insufficient to overcome the inertia of catheter deflection control mechanism 20. That is, catheter deflection actuator 58 may bind against catheter deflection control mechanism 20, causing relative rotation between catheter control handle 28 and catheter deflection actuator 58. This relative rotation may result in uncommanded tensioning of one or more pull wires 50, inadvertently deflecting distal end 52 of catheter 12.

To maintain a substantially constant deflection as catheter 12 rotates, therefore, controller 24 may be operatively coupled to both rotation servo mechanism 60 and deflection servo mechanism 22. Controller 24 is adapted to control at least one of deflection servo mechanism 22 and rotation servo mechanism 60, and preferably to simultaneously control both deflection servo mechanism 22 and rotation servo mechanism 60, to maintain a substantially constant deflection of distal end 52 as catheter receiving portion 26 and catheter 12 rotate. For example, as controller 24 commands rotation servo mechanism 60 to rotate catheter receiving portion 26, controller 24 may simultaneously command deflection servo mechanism 22 to actuate catheter deflection control mechanism 20 to counter-rotate, thereby substantially eliminating relative rotation between the catheter deflection actuator 58 and catheter control handle 28, helping to maintain a substantially constant deflection of catheter 12. Alternatively, as controller 24 commands rotation servo mechanism 60 to rotate catheter receiving portion 26, it may simultaneously command deflection servo mechanism 22 to decouple catheter deflection control mechanism 20 from catheter deflection actuator 58, thereby permitting catheter deflection actuator 58 to rotate freely with catheter control handle 28. In either case, controller 24 may be configured to eliminate the need to couple deflection servo mechanism 22 and rotation servo mechanism 60 through a mechanical transmission system such as a differential. Further, though described herein as a single controller adapted to control the translation, deflection, and rotation servo mechanisms 18, 22, 60, multiple controllers may be used without departing from the spirit and scope of the present invention.

An introducer 62, preferably a steerable introducer, and most preferably an Agilis™ steerable introducer, may be provided as part of robotic surgical system 10. A proximal end 64 of introducer 62 is preferably stationary, while a distal end 66 of introducer 62 extends into a patient (not shown for clarity) to a location proximate a target site (the term “target” is used herein to refer to a location at which treatment or diagnosis occurs). Introducer 62 may be steerable via a robotic control system 68 including at least one servo mechanism 70 adapted to control distal end 66 of introducer 62 in at least one degree of freedom. Preferably, robotic control system 68 includes three servo mechanisms 70 adapted to control distal end 66 of the introducer 62 in three degrees of freedom (translation, deflection, and rotation), resulting in a total of six degrees of freedom for robotic surgical system 10, and at least one controller 72 adapted to control servo mechanisms 70. Similar control principles may be applied to steerable introducer 62 as are described herein with respect to robotic surgical system 10 and medical device 12.

One of ordinary skill in the art will appreciate that the deflection of distal end 52 of catheter 12 is a function not only of the input to catheter deflection actuator 58 (i.e., the selective tensioning of one or more pull wires 50), but also of the extent to which catheter 12 is advanced beyond a generally rigid sheath, such as introducer 62. That is, the further distal end 52 of catheter 12 is advanced beyond distal end 66 of introducer 62, the greater the deflection of distal end 52 of catheter 12 will be for a given input at catheter deflection actuator 58.

It is therefore desirable to calibrate the deflection of distal end 52 of catheter 12 in terms of both catheter deflection control mechanism inputs and extensions of catheter 12 beyond distal end 66 of introducer 62. By robotically actuating catheter deflection control mechanism 20 between extremes (e.g., commanding a complete rotation of catheter deflection actuator 58) and measuring the resulting deflection of distal end 52 of catheter 12 (e.g., using a localization system), catheter deflection control mechanism inputs may be correlated with deflections of distal end 52 for a given extension of catheter 12 beyond distal end 66 of introducer 62. A similar process may be performed for a multiple different extensions of catheter 12 beyond distal end 66 of introducer 62, resulting in a family of calibration curves relating catheter deflection control mechanism inputs to deflections of distal end 52 of catheter 12. Each curve corresponds to a particular extension of catheter 12 beyond distal end 66 of introducer 62; the amount of extension of catheter 12 beyond distal end 66 of introducer 62 may be derived, at least in part, from the amount of translation of catheter holding device 16 relative to track 14.

To create a substantially sterile field around catheter 12 outside the patient's body, an expandable and collapsible tubular shaft 74 substantially surrounds at least a portion of catheter 12, such as the region of catheter 12 between catheter holding device 16 and proximal end 64 of introducer 62. Preferably, shaft 74 is sterilized before use along with other relevant components of robotic surgical system 10. As catheter holding device 16 translates to advance catheter 12 into the patient (i.e., to the right in FIG. 1), tubular shaft 74 collapses upon itself. Contrarily, as catheter holding device 16 translates to retract catheter 12 from the patient (i.e., to the left in FIG. 1), tubular shaft 74 expands. Preferably, tubular shaft 74 is assembled from a plurality of telescoping tubular elements 76. It is contemplated, however, that tubular shaft 74 may alternatively be an accordion-pleated or other expandable and collapsible structure.

As depicted in FIGS. 7 and 8, robotic surgical system 10 may be employed to robotically navigate catheter 12 into and through the patient and to one or more sites, which may be target sites, within the patient's body by actuating one or more of translation servo mechanism 18, deflection servo mechanism 22, and rotation servo mechanism 60 (if present) via controller 24. Robotic surgical system 10 may operate automatically according to a computerized program as executed by controller 24 (FIG. 7). It is also contemplated that the user, who may be a surgeon, cardiologist, or other physician, may control robotic surgical system 10 through an appropriate set of controls 78, such as a three-dimensional joystick (e.g., a joystick with three input axes), a steering yoke, or another suitable input device or collection of such devices permitting the user to robotically steer catheter 12 (FIG. 8).

As described above, catheter 12 can be quickly and easily disconnected from catheter holding device 16. Thus, if the user desires to manually control catheter 12 at any point during the procedure, the user may disconnect catheter 12 from the catheter holding device 16 as described above. The user may navigate catheter 12 manually for as long as desired, and then replace it into catheter holding device 16 and resume robotic control. FIG. 9 illustrates the user manually operating catheter 12 after having removed it from catheter holding device 16.

In some embodiments of the invention, multiple robotic surgical systems controlling multiple medical devices may be employed during a procedure. For example, a first robotic surgical system may control an ultrasonic imaging transducer, while a second robotic surgical system may control an ablation catheter. A single controller, or multiple cooperating controllers, may coordinate the multiple medical devices and the multiple robotic surgical systems, for example in conjunction with a single localization system, or alternatively by utilizing data from the ultrasonic imaging transducer to control the movement of the ablation catheter.

Robotic surgical system 10 facilitates precise and accurate navigation of medical device 12 within the patient's body. In addition, since medical device 12 is manipulated primarily robotically, the physician will experience considerably less fatigue during the surgical procedure. Furthermore, robotic control permits a substantially increased degree of complexity in the control and actuation mechanisms that may be incorporated into medical device 12 over those that may be used in a medical device 12 intended solely for human control, enabling an increase in the versatility of medical device 12.

It is also contemplated that the user operating robotic surgical system 10 may be remote from robotic surgical system 10. For example, an expert physician in one city may control robotic surgical system 10 located in a second city via a computer network, such as the Internet.

Contact Sensing

FIG. 10 schematically illustrates a surgical system 80 equipped to sense contact between a probe, such as catheter 12, and a tissue surface 82, such as a cardiac wall. Probe 12 includes a sensor or instrument 84 carried thereon, preferably at distal end 52 of probe 12, for measuring the value of a parameter (referred to herein as P) of tissue surface 82 either periodically (that is, with a relatively fixed interval between measurements) or episodically (that is, with a variable interval between measurements). Preferably, sensor 84 is an electrophysiology sensor capable of measuring one or more electrophysiology characteristics, including, but not limited to, impedance, phase angle, electrogram amplitude, optical feedback, and ultrasonic feedback.

To facilitate precise determination of the distance traveled by probe 12 between measurements of the tissue parameter (referred to herein as Δs), a precisely calibrated system is utilized. The precisely calibrated system may be a robotically controlled system to move probe 12 within the patient's body, such as robotic surgical system 10 described herein. It is also contemplated that measurements of the position of probe 12 within the patient's body may be made using a precisely locally- or universally-calibrated positional feedback (i.e., localization) system 86 in conjunction with a location or position electrode 88 carried on probe 12. Preferably, the positional feedback system is the Ensite NavX™ system of St. Jude Medical, Inc., which includes pairs of electrodes 90 defining measurement axes by which the position of probe 12 may be measured. One of ordinary skill in the art will appreciate that other localization systems, such as the CARTO navigation system from Biosense Webster, Inc., may also be employed. Only one pair of electrodes 90 is illustrated; one of skill in the art will appreciate that additional pairs of electrodes 90 may be used if additional measurement axes are desired.

A processor monitors the value of the tissue parameter measured by sensor 84 as probe 12 moves within the patient's body. The processor may be incorporated in a computer system 92. For purposes of this disclosure, a single processor within computer system 92 will be referred to, though it is contemplated that multiple computer systems 92 and/or multiple processors within a single computer system 92 may be used to practice the various aspects of the present invention. Further, one or more processor functions described herein may be integrated in a single processor without departing from the scope of the present invention.

As described above, probe 12 may be moved by a robotically-controlled system capable of precise movements on the order of less than about 5 mm, more preferably on the order of less than about 2 mm, and most preferably on the order of less than about 1 mm. Alternatively, the movements of probe 12 are precisely measured by a positional feedback system 86 with a margin of error of less than about 5 mm, preferably less than about 2 mm, and more preferably less than about 1 mm. For a given, precisely determined Δs (e.g., as precisely moved by robotic surgical system 10 or precisely measured by positional feedback system 86), a corresponding amount and rate of change in the tissue parameter between measurements can be anticipated for a situation where there is no change in the proximity or degree of contact between probe 12 and tissue surface 82.

The processor monitors the tissue parameter for an indicator of proximity or degree of contact between probe 12 and tissue surface 82 and indicates a change in the proximity or degree of contact between probe 12 and tissue surface 82 based on the monitored tissue parameter. In particular, the processor reports the change in either proximity or degree of contact based on either the amount of change in the tissue parameter or the rate of change in the tissue parameter between measurements, and preferably between successive measurements, thereof. The term “proximity” refers to the relationship between probe 12 and tissue surface 82 when probe 12 is not in contact with tissue surface 82; it is, in lay terms, a measure of how close probe 12 is to tissue surface 82. The term “degree of contact” refers to the relationship between probe 12 and tissue surface 82 when probe 12 is in contact with tissue surface 82; it is, in lay terms, a measure of how hard probe 12 is pressing into tissue surface 82.

A contact sensing method is illustrated in the high-level flowchart of FIG. 11. Probe 12 is navigated into the patient's body and into meaningful proximity with tissue surface 82 in step 100. The term “meaningful proximity” refers to probe 12 being sufficiently close to tissue surface 82 such that sensor 84 can capture useful electrophysiology information about surface 82, and thus encompasses both contact and non-contact relationships between probe 12 and tissue surface 82.

Once inside the patient's body, probe 12 is moved using a calibrated system, such as robotic surgical system 10, moved and located using a calibrated system, such as positional feedback system 86, or both. As probe 12 moves, the tissue parameter at distal end 52 of probe 12 is measured, either periodically or episodically, using sensor 84 (steps 102, 104, and 106). An amount of change (ΔP) in the measured tissue parameter between successive measurements (P_(n) and P_(n+1)) is calculated in step 108. The processor then indicates a change in proximity or degree of contact between probe 12 and tissue surface 82 based upon the amount of change in the measured tissue parameter in step 110. That is, the processor provides the user and/or controller 24 controlling robotic surgical system 10 with an indication of either “change” or “no change” in the proximity or degree of contact based upon the amount of change in the measured tissue parameter. If desired, the process may be repeated as probe 12 continues to move through the patient's body by setting P_(n)=P_(n+1) (step 112) and moving probe 12 to a new location (step 104) where a new P_(n+1) is measured (step 106).

A number of algorithms may be used to identify the change in proximity or degree of contact between probe 12 and tissue surface 82 in step 110. In a first algorithm, illustrated in FIG. 12a , the amount of change in the measured tissue parameter (ΔP) is compared to a predetermined range of values ranging from a lower limit (LL) to an upper limit (UL) in step 114 a. (In FIGS. 12a through 12o , absolute values are used in order to account for potential negative values of ΔP.) A change is indicated when the amount of change in the measured parameter falls outside the predetermined range of values (step 116 a); no change is indicated when the amount of change in the measured parameter falls within the predetermined range of values (step 118 a).

The predetermined range of values (that is, either or both of UL and LL) may be user selectable, and may correspond generally to the anticipated amount of change in the measured tissue parameter between measurements when there is no change in the proximity or degree of contact between probe 12 and tissue surface 82 for a given Δs. “Predetermined” is used herein to refer to values that are set in advance of applying the contact sensing algorithm; for example, the values (i.e., UL and LL) may be based upon a percentage variation in the anticipated change in the measured tissue parameter, which percentage may also be user selectable.

In other algorithms, the amount of change in the measured tissue parameter is compared to a change threshold, with the change indication based upon whether or not the measured tissue parameter crosses the change threshold. For example, as shown in FIG. 12b , the change threshold may correspond generally to the maximum anticipated amount of change in the measured tissue parameter between successive measurements for a given Δs (ΔP_(MAX)). Thus, no change in proximity or degree of contact would be indicated when the amount of change is less than the change threshold, and a change in proximity or degree of contact would be indicated when the amount of change is greater than the change threshold. It is also contemplated that the algorithm may be modified as shown in FIG. 12c , such that the threshold corresponds generally to the minimum anticipated amount of change in the measured tissue parameter between successive measurements for a given Δs (ΔP_(MIN)), which would reverse the conditions for indicating change or no change in proximity or degree of contact. The change threshold may be user selectable, and may be calculated as a percentage variation in the anticipated amount of change in the measured tissue parameter for a given Δs, which percentage may itself be user selectable.

In still other algorithms, the change in proximity or degree of contact is indicated based upon a rate of change in the measured tissue parameter with respect to either the time between measurements (ΔP/Δt) or the distance traveled by probe 12 between measurements (ΔP/Δs). The rate of change may also be calculated as a derivative of the measured tissue parameter with respect to time (dP/dt) or probe distance traveled (dP/ds). The rate of change may be calculated as a first derivative of the tissue parameter, a second derivative of the tissue parameter, or any further derivative of the tissue parameter. One of skill in the art will recognize that any of these variables may be calculated from the amount of change in the measured tissue parameter and the time between measurements or the precisely determined distance traveled by probe 12 between measurements. The decision processes for indicating change in proximity or degree of contact based upon rate of change variables are substantially analogous to the algorithms described with respect to the amount of change in the measured tissue parameter (i.e., comparison to a predetermined range of values or comparison to a rate of change threshold). These alternative algorithms are illustrated in FIGS. 12d -12 o.

In FIGS. 12b-12o , steps analogous to those depicted in FIG. 12a are identified by a common reference number and an updated letter designator. That is, step 114 b, shown in FIG. 12b , is the analogue to step 114 a for the algorithm illustrated in FIG. 12b ; step 114 c, shown in FIG. 12c , is the analogue to step 114 a for the algorithm illustrated in FIG. 12c ; and so forth.

FIG. 13a is a representative chart of the measured tissue parameter as a function of time (t) or probe distance traveled (s), while FIG. 13b illustrates the derivative of the curve of FIG. 13a . Initially, in region 120, there is no change in proximity or degree of contact, so P varies only slightly. ΔP is thus quite small, so ΔP/Δt, ΔP/Δs, dP/dt, and dP/ds vary slightly about zero (dP/dt and dP/ds are illustrated in FIG. 13b ).

When a change in proximity or degree of contact occurs, such as at point 122, P experiences a substantial change in a very short interval of time or probe distance traveled. ΔP/Δt and ΔP/Δs are thus quite large, and the curve of FIG. 13b illustrating the derivative of the measured tissue parameter exhibits a corresponding spike 124 before returning to varying slightly about zero in region 126. A second spike 128 corresponds to a point 130 where another change in proximity or degree of contact occurs.

The contact sensing methods described above are useful in monitoring for a change indicative of probe 12 making contact with tissue surface 82, a change indicative of probe 12 breaking contact with tissue surface 82, or a change indicative of a change in the degree of contact between probe 12 and tissue surface 82. In the lattermost case, the method may provide an indicator of whether probe 12 is beginning to break contact with tissue surface 82 or is potentially being traumatically driven into tissue surface 82. This information may be used by the user and/or robotic surgical system 10 (e.g., controller 24) as feedback to adjust the movement of probe 12 to maintain a particular degree of contact with tissue surface 82 on an ongoing basis in order to improve the quality or efficiency of the medical treatment. For example, in an ablation procedure for the treatment of atrial fibrillation, one of ordinary skill will readily appreciate that a spike in a derivative of the tissue parameter, as shown in FIG. 13b , may indicate that the ablation catheter has broken contact with the cardiac surface and is therefore no longer creating a substantially continuous lesion and that appropriate corrective action is necessary to bring the ablation catheter back into contact with the cardiac surface. As another example, in a surface modeling procedure, the spike may indicate that the modeling probe has broken contact with the surface being modeled such that the collection of geometry points should be suspended in order to avoid capturing erroneous data.

Although several embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention. For example, the robotic surgical system 10 may be modified to incorporate additional servo mechanisms and controllers operating on additional degrees of freedom.

Further, though the contact sensing methodology has been described in connection with a robotically controlled medical device, it could also be implemented in a manually controlled medical device. It should also be understood that, rather than utilizing absolute values in the various contact sensing algorithms described herein, the thresholds or limits may be appropriately adjusted to compensate for negative values of ΔP, for example by taking the opposite of all thresholds or limits and reversing the comparator (i.e., changing < to >) upon detecting that ΔP is less than zero.

In addition, one of ordinary skill in the art will appreciate that, though the devices and methods disclosed herein have been described in connection with the treatment of atrial fibrillation, and in particular in connection with the creation of lesions of ablated tissue, they may be used to administer other therapies or to perform other diagnostic procedures.

Further, the devices and methods disclosed herein are capable of use both epicardially and endocardially.

All directional references (e.g., upper, lower, upward, downward, left, right, leftward, rightward, top, bottom, above, below, vertical, horizontal, clockwise, and counterclockwise) are only used for identification purposes to aid the reader's understanding of the present invention, and do not create limitations, particularly as to the position, orientation, or use of the invention. Joinder references (e.g., attached, coupled, connected, and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other.

It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims. 

What is claimed is:
 1. A method of monitoring contact between a probe and a tissue surface, the probe having an electrophysiology sensor at a distal end thereof, the method comprising: placing the probe in proximity to the tissue surface; robotically moving the probe; measuring an electrophysiological tissue parameter at the distal end of the probe using the electrophysiology sensor, wherein the electrophysiological tissue parameter comprises phase angle; calculating a rate of change in the measured electrophysiological tissue parameter with respect to a distance traveled by the probe; and indicating a change in proximity or degree of contact between the probe and the tissue surface based upon the rate of change in the measured electrophysiological tissue parameter with respect to the distance traveled by the probe.
 2. The method according to claim 1, wherein the step of indicating a change in proximity or degree of contact between the probe and the tissue surface based upon the rate of change in the measured electrophysiological tissue parameter with respect to the distance traveled by the probe comprises: indicating no change when the rate of change in the measured electrophysiological tissue parameter falls within a pre-determined range of values; and indicating a change when the rate of change in the measured electrophysiological tissue parameter falls outside the pre-determined range of values.
 3. The method according to claim 2, wherein the pre-determined range of values is user-selectable.
 4. The method according to claim 1, wherein the step of indicating a change in proximity or degree of contact between the probe and the tissue surface based upon the rate of change in the measured electrophysiological tissue parameter with respect to the distance traveled by the probe comprises: comparing the rate of change in the measured electrophysiological tissue parameter to a rate of change threshold; indicating no change when the rate of change in the measured electrophysiological tissue parameter is less than the rate of change threshold; and indicating a change when the rate of change in the measured electrophysiological tissue parameter is greater than the rate of change threshold.
 5. The method according to claim 4, wherein the rate of change threshold is user-selectable.
 6. A surgical system, comprising: a probe for introduction into a body of a patient; a robotically-controlled system to move said probe within the body of the patient; an electrophysiology sensor carried on said probe for measuring a parameter of a tissue surface, wherein the parameter comprises phase angle; and a processor programmed to monitor the parameter and indicate a change in proximity or degree of contact between the probe and the tissue surface based on a rate of change in the parameter relative to a distance traveled by the probe. 